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08 check Malibu catalytic converter issues

I have an 08 chevy Malibu. The code for the issue was my catalytic converter had gone bad. I had someone’s clear the code, then used cataclean to try and resolve the issue but the code popped back up. Can I use it again to try and resolve the issue or am I SOL and need to buy a new part?

What is the code? How many miles?

Sure, try Cataclean again, it didn’t work the last time, but why not? It’s a few bucks in the tank versus a few hundred (or more) on new a new cat(s).

There is no code that tells you that your cat is bad!!!

There is a pre cat o2 sensor and a post cat o2 sensor. If the signal from one of these sends a signal to the ECM, and that signal is not within the parameters that the computer expects…the computer will throw a code.

without you telling us what the actual code was, we can only guess.
Your problem could be a sticky injector, a sticky valve, a vacuum leak, misfires, or any one of other causes.

A code never tells you what part to replace, it only gives you a clue as to where to start your diagnosis and you work back from that point.
Look at it this way. If you had a garden hose out and you squeezed the trigger on the spray nozzle and nothing happened…would you go out and buy a new spray nozzle. No you would go and make sure that the hose is actually on the outside faucet. If it is then you would check to be sure the faucet is actually turned on.


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Get a shop with a Chevy scan tool to look at the pre-cat and post cat O2 sensor waveforms. That way you’ll know for sure if the cat itself is faulty or there’s a problem with the sensors or the wiring. It seems unlikely any chemical treatment will return a faulty cat back to working order, at least not for any length of time. Unless you are just trying to sneak past an emissions test in order to renew your registration, suggest to not waste time and money trying to renew the cat. Best to focus on whether the cat is actually bad or not, using the above method. @Tester here recently posted what the scan tool display looks like when they make that test, but I don’t recall where that was posted.

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It can’t.
(for the OP) Catalytic converters are basically a canister containing a ceramic honeycomb sputter-coated with an exotic metal, platinum-palladium. When the exhaust stream comes in contact with the coating, heated from the exhaust stream, the catalytic converter performs its chemical magic. Catalyst by definition means an element that causes a change in something without itself changing. However, in order for the exotic metal to cause the change, the molecules in the exhaust stream must come in direct contact with the metal.

Cat converters fail when the precious metal becomes too permeated or coated with exhaust elements (such as carbon) for the exhaust stream to come in direct contact with it. No additive will clean these contaminants via their being added to the fuel. Any that survive the explosion in the combustion chamber will only travel through the converter with the exhaust… and more than likely they might actually add unwanted elements to the exhaust stream that might further coat the precious metals that make the converter work.

In summary, once the converter is contaminated, it’s shot. Forever.

Having said that, George’s recommendation to find a shop that can and will check the actual oxygen sensor waveforms is the way to go. A bad oxygen sensor can suggest a bad cat converter erroneously. The sensors are how the ECU monitors the converter performance.

NOTE: believe it or not, this is a SIMPLIFIED explanation of how a cat converter works, just for the OP’s sake. I skipped the chemistry. Felt this was enough for the OP to absorb.

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Informative post there TSM :slight_smile:

For the OP, here’s the link to what the waveforms look like on the scan tool when a shop tests a cat.

the substrate in the cat is contaminated by fuel deposits/carbon. and nothing will remove these deposits? what does catclean say it does to increase cat performance?

Remember the line in Cher’s song:

“grampa did whatever he could,
preached a little gospel,
sold a couple bottles of Doctor Good”

Catclean is the modern version of “Doctor Good”.

Over the many years I have participated on this board, there have been mechanics who have said they never have replaced the cat; it has always been the sensors. Unless extreme contamination from an oil burner or something like that. And, in that case, a new cat is going to be wasted.

Other mechanics have said it is always the cat when there is the dreaded P0420.

I have also found a number of people who have taken off the cat, and soaked it overnight in water with dish detergent. And, in the morning, there are white things floating in the water. And, the cat works then.

However, do not expect any professional mechanic to try this for more than one valid reason.

Also at times, there is enough corrosion on the converter that it is nearly impossible to get it off and back on.

If a mechanic tells you, the P0420 is ALWAYS the cat, take your car and run. He is either an idiot or a thief. As stated here, the best of all will be the mechanic who actually looks at the outputs of the sensors.

In my personal experience, my 2002 Sienna, which is now parked in Texas due to changing Mexican import laws, I had P0420 code a number of times. In every case, replacing the sensor or sensors fixed it. It had 222,000 miles on it when parked.

This is the first I’ve heard this idea that I can remember. Admittedly, it may be in an old thread that I don’t remember. :stuck_out_tongue_winking_eye:
Did they claim to have blown it out backwards after soaking?

I don’t think so. I first heard this on a Youtube video produced several years ago by Scotty Kilmer, who at that time had program like a mini-cartalk on a Houston station. That was the last option he listed. The first one was to put lacquer thinner in your gas tank. That stirred up this board like tossing a rock into a hornet’s nest. A search for Scotty Kilmer should bring it up. I did find postings for people who tried it and it mostly worked for them. There were also a lot of people who said it could not work, and they didn’t try it.

There was one, an older Honda, where it did damage. No newer cars reported that.

Soaking it would not likely damage the fuel system, of course. The problem with soaking it is getting it off and back on. If not too much corrosion might not be impossible.

Apparently the element does not wear out, which is what catalytic means But, it can be mechanically damaged, or I suppose burned up if it gets white hot. Or, as the soaking would indicate, be contaminated.

But, I find no evidence from any scientific source that in normal use, it “wears out” as some mechanics claim. Again, I say that is what catalytic means

I repeat that I have little experience with this. My 2002 Sienna had a lot of P0420 failures and in every case the sensors fixed it. It was almost all highway driving outside the Snow Zone, and the motor did not burn oil.

Re-reading I can see I did not adequately answer your question. The video showed the small pieces of white stuff floating out of the converter by themselves. I assumed they were formed by some strange phenomenon and covered the grid of rare earth so the cat did not work correctly because the grid did not contact the gases coming in, from a normally working system. And, when those white things were taken away, the grid again had exposure to the gases and they were burned up.

But if you’ve got a car that will not pass the tailpipe test because the cat is no longer doing its job, and there is no excessive oil consumption, overheating, no exhaust leaks, no faulty oxygen sensors, etc. . . . in other words, there are no factors that led to the cat’s demise . . . what would YOU call it?

Even though the term “worn out” may not be technically accurate, it sure seems to describe the situation quite nicely

And let’s suppose that the catalytic converter was replaced, and the car then passed the tailpipe test with flying colors

To be clear, I’m not talking about P0420 codes. Forget about oxygen sensors and codes for a moment. I’m talking about a scenario where the 5-gas analyzer tells you crystal clear that the cat isn’t doing what it’s supposed to

I’ve seen these scenarios a few times

By the way, I have no opinion about soaking cats, because I’ve never heard about such things, outside of this particular website

Now we can get back to codes . . .

And this is not the scenarios you’ve brought up repeatedly

I’ve seen a few cases where the cat’s not doing its job, and the 5-gas analyzer will prove this conclusively. Yet there never was a P0420, not even a pending code

My point is that the codes and the oxygen sensor don’t always tell the whole story

And I’ll bet some of the other pro wrenchers on this forum have similar stories to tell

I’m not saying you’re wrong. In fact, I value your experience and like reading what you have to say, in spite of the fact that we’ve disagreed in the past, and probably will do so in the future

I’m just coming at things from a different angle, and offering my own opinions and experiences

In my own 75 years of life experience, I have learned that when two people disagree about semantics, there is usually a reason. Of course, a too common reason is someone is being anal, like the people who freak out when an old posting is brought up FROM THE INCREDIBLE REPOSITORY OF KNOWLEDGE THAT THIS BOARD REPRESENTS. They don’t seem to understand that a 2008 posting about a new 2008 car may still be relevant today. I sometimes think they look at postings as a current event, and not as an addition to the repository of knowledge.

But there are other reasons as well, including cultural background, language, and what one’s goals are. In your case, correct me if I am wrong, your goal is to repair a vehicle as efficiently as possible and make the customer happy. And, sometimes the latter goal would require you to refuse a job where customer satisfaction is statistically improbable.

You and I are both bilingual. Or, better stated, you are bilingual (your English is flawless) and I am struggling. I tell my English students that my Spanish is not exactly Spanish, but they already know it when I tell them Buenos Dias. :smiley: In most cases, bilingual also means bi-cultural. And, that affects how we interpret terms and words.

My goal is to try to disseminate the fact that too many of the poorer mechanics insist P0420 ALWAYS means replace the cat. I think Toyota California cats can run in the area of several thousand dollars. We have had posters tell us that is the price range they encountered.

In my over fifty years of dealing with mechanics, I have learned that the worst mechanics are almost always angry and physically belligerent, even without a disagreement. And, if you disagree with a low-life knucklehead who tells you P0420 ALWAYS means replace the cat, you will be lucky to escape without violence. We have had a lot of posters report exactly that from mechanics; I mean the ALWAYS claim, not the violence.

Cats are simply not a wear item. All the data I have encountered indicates they become damaged, or become contaminated. (Of course, I forgot plugged which is totally a different matter, a subset of contamination.) Once, someone, considering the recycle value of a cat, must have worked at a salvage yard, opened some up and he found either contamination on the rare earth grid, or whatever you call it. And, he also found some where the grid was ripped up as if something hit that cat and the shock damaged the insides.

In your case, you know to look at the sensors and thus you KNOW if the cat is bad. And, from a commercial viewpoint, as long as you are not blindly replacing good cats from ignorance, you are doing a good, no, great job. But, the low-life knuckleheads replace lots of good cats.

And, if they come here, they are going to say, “I knew I was right. Top mechanics on Cartalk say cats wear out. That will be $1500 and while we are at it, we might as well replace all the sensors so you start out perfect. Make that $2100.” AKKKK!!!

Since the short attention span guys are already well asleep :smiley: I am going to share something I never shared before. I was a diagnostic technician in a high tech factory for over 30 years. I was never allowed to do my own parts replacement. If the company wanted 10 new degreed accountants, they would call the state employment office which would send over a packet of resumes of degreed accountants.

If they wanted a new production technician, entry level for one of us, they packed their bags. A trip might send them to Michigan; Minnesota; and also Texas and Florida, and they still might come back with no new hire. That was just using electronics and basic diagnostics as a testing standard.

Those who soldered had a week long school in the company when hired. Government soldering specs were so high that most who replaced our bad parts usually had many years experience soldering to government specs. My wife, who was one of them, said they had to go back to solder school once a year, and depending upon their certification level, that annual school could be from one day to a week. And, their work was inspected with a microscope.

It was impossible to hire a number of electronic techs who could also pass a test to government standards for soldering. They didn’t even try.

I have read some folks who think as cars get more computerized it might be necessary to make the same labor split, a few really high level techs who can handle the computerization, and others who replace the parts specified. I don’t expect to see that in the near future. The automotive repair industry seems to run on financial exploitation of the mechanics, but what do I know?

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That is true, to a degree

A CARB-certified direct fit cat, which typically includes a significant portion of the exhaust system, including pipes, flanges, oxygen sensor bung, etc., can fall in the price range you mentioned, expecially if it’s bought from the dealer and is perhaps a configuration which includes both cats on a V-type engine. I’m thinking of a y-type exhaust on certain V engines, which might include the cats for both banks, on a single assembly. :heavy_dollar_sign:

But there are alternatives. On the bureau of automotive repair, there exists a list of approved cats. It’s a lengthy list, and not easy to digest, but on the low end, some of the approved products are weld-in type cats with a more modest price tag. In my opinion, the quality is middling, but it might be the silver bullet, for a person of limited means who just needs to keep their 12 year old vehicle running to get to/from work, or drive the kids to/from school. And you’ll have to find somebody skilled enough to do an acceptable job of welding that cat in

The middle ground would be an aftermarket carb-approved part. Eastern catalytic comes to mind. I believe they have a rather extensive offering, and they should offer parts for common vehicles

The frustrating thing . . . from a customer’s perspective, I suppose . . . would be that scenario I described. The one in which the cat is not effective enough to pass the tailpipe test, yet there are no codes and the required readiness monitors are complete. If the customer’s car was a little newer and subject to the simpler plug-in type of test, in all likelihood they would have received their new certificate, assuming their emissions components are present and unaltered.

Those other scenarios where the 5-gas analyzer verifies the cat’s ineffectiveness, absent any oil burning, overheating, exhaust leaks, etc. are also interesting. To a degree, it’s as if the cat was hollowed out, yet a physical inspection reveals everything present and accounted for. From a financial standpoint, I can understand why somebody would want to follow Scotty Kilmer’s advice. The customer has nothing to lose, but don’t expect a recommendation from me. One could perhaps consider that to be tampering, but how would the smog inspector go about proving that, and for that matter, what would lead him to believe it had even occurred?

This is hearsay . . .

Several years ago, one of my colleagues was speaking about one of his former jobs. He was working as a mechanic for a sheriff’s department, both before and after privatization. Apparently, a shop foreman with reasonable diagnostic skills had been hired, at a slightly higher rate, versus the others, who were largely expected to be parts replacers. The regular mechanics were expected to relegate all diagnosis to the shop foreman, while they continued to perform the simpler duties, such as oil changes, brake pad replacement, etc.

There is also some truth to that, again in my opinion . . .

There have been many instances in which “the system” is heavily favored against the mechanic’s best financial interests. When there is any type of misunderstanding, argument, etc., the final bill is often discounted, at the mechanic’s expense. Clearly, there is also less money coming in for the shop in general, but the fact remains that the mechanic walks home with less money than he was led to believe he’d be getting. Not exactly a pleasant situation. All the explaining in the world can’t make him feel good about it.

But that’s enough ranting for now

I thoroughly enjoyed reading your brief description of your career :smiley_cat:

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Not necessarily. The ceramic honeycomb on which the platinum-palladium is sputter-coated can be physically damaged, typically by extreme heat due to too-lean operation or by sticking exhaust valves allowing “backfiring” (a technically incorrect term) into the converter. When this happens, the ceramic can be fractured, forming a plug of broken innards at the canister’s exit.

Note that ceramics hold heat. That works to the advantage of the process under normal circumstances, as the platinum-palladium has to approach 400F to begin to effect the nitrogen-oxides. Modern designs place the converters at the exhaust manifold so they’ll get hotter faster, reducing emissions. But in the event of extreme cylinder temps, it works as a detriment to the converter’s ceramic honeycomb.

Other than that detail, a minor one, you’ve written a great post.
Cat converters don’t “wear out”. What happens is that the platinum-palladium coating becomes contaminated with exhaust byproducts, and the coating cannot effect the nitrogen-oxide unless it be contacted intimately, molecule-to-metal, and the coating begins to create a barrier to this intimacy. Effectivity drops accordingly.

And you’re right: catalysts cause change in something else without themselves changing. That’s the very definition of “catalyst”. It applies to the platinum-palladium too.

Notice the difference between detailed information here on P0420 and related topics, vs. knuckleheads who actually believe P0420 simply means replace the cat! That is why I call this board an incredible repository of information.

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I agree. I learn stuff here all the time, and have been for many years.


Again sorry, but I didn’t read all the responses. All I know is I ruined my cat in about 5 minutes with a misfire. I don’t know what the exact code was but Onstar said it was for the cat. I still was under warranty so the GM dealer said they would clear the code and then if it came back right away they would replace the cat. It came right back and they replaced the $700 cat. So there must be some code that indicates a bad cat.